The present invention relates to a retrievable tension-set packer used by itself, or in conjunction with a retrievable tension-set bridge plug, for field testing of oil well casings.
As is well known in the oil field industry, underground oil well casings are subjected to integrity testing in selectively isolated zones or sealed off areas for a variety of activities including acidizing, fracturing, squeeze cementing, or for other testing purposes. These types of activities are generally conducted through separate tubing that is lowered down within the oil well casing. It is therefore, essential and necessary that a pressure tight seal be made at displaced locations within the casing, above and below the area to be tested, such as a casing fracture or perforation point, in order that the desired activity can be adequately performed.
In order to establish a sealed off area below the selectively isolated zone in the oil well casing, one typical construction that was used for approximately twenty years, is the cup-type, pressure-set, retrievable bridge plug, which is manufactured by Elder Oil Tools, Incorporated of Yorktown, Tex. This particular type of bridge plug employs a pair of upwardly and downwardly spaced sealing cups which, when located in position within the oil casing, and either activated under pressure or by rotation, provide compression of the sealing cups, in order to bias them against the inner wall of the casing, and thereby provide a sealed location, generally at the lower end of the selectively isolated zone to be tested. Because of the corroded, pitted or, otherwise deteriorated inner wall surface of the casing, this earlier style of bridge plug had inherent problems in that the sealing cups have not generally provided an effective seal. As a result, leakage occurs because the pressure cannot be retained, and therefore, the testing in the selectively isolated zone can not be effectively accomplished. The Environmental Protection Agency of the U.S. government has also issued regulations allowing only a 10% loss of pressure in the selectively isolated zone within a thirty minute period Due to the aforementioned deterioration of the casing in many wells, this type of tool is unable to create the necessary pressure seal to successfully complete EPA testing.
In order to seal off the casing above the selectively isolated zone to be tested, generally a retrievable weight-set or tension-set packer could generally only be employed in rather deep wells because of the necessity of requiring approximately eight thousand pounds of pressure, through the weight of the tubing within the well, in order to achieve compression of elastomeric rings or components against the internal wall surface of the casing, for setting the packer in the desired location above the selectively isolated zone to be tested. While weight-set or tension-set packers, made operative by the heavy weight of tubing within the oil well casing, are effective for deep wells, i.e., those over 3,000 feet in depth, they are generally not capable of being used in a shallow well, that is. those that extend downwardly to approximately 1500 feet, but generally no lower than 3,000 feet.
In order to satisfy the new EPA regulations for integrity testing of well casings, a new tension set retrievable bridge plug has been developed by Arrow Oil Tools, of Tulsa, Oklahoma, which is a tension-set, packer-type retrievable bridge plug that uses mechanical operation from the surface to set the bridge plug in the desired sealed location below the selectively isolated zone to be tested. These newly developed bridge plugs require either a one-quarter turn left-hand set and right-hand release, or a one-quarter turn right-hand set and left-hand release. In order to be used in conjunction with the newly developed retrievable tension-set bridge plug, a retrievable tension-set packer that is used above the selectively isolated zone to be tested, must likewise be tension-set and released by the one-quarter left or right-hand turn as aforesaid. Thus, while it may be possible to use the retrievable bridge plug and retrievable packer together in setting and re-positioning of the aforementioned units at various positions along the oil well casing, there is little possibility, with existing designs, for any variation in the displacement between these two components, which makes it almost impossible to achieve the proper setting of the bridge plug and packer at locations above and below the area to be tested. In addition, while they are capable of cooperative movement and re-positioning together as a unit within the oil well casing, they are not capable of cooperative removal. Hence, the only way to remove one or both of these components from the casing, after the testing has been completed, is to ream them out or otherwise destroy them through other well drilling components or instrumentation.
The aforementioned one-quarter turn setting/release of the packer and bridge plug combination is accomplished through the use of a bayonet lock design, employing a pair of pins in cooperating elements which fit into inverted and aligned J-shaped slots, such that the pins, when within the J-slots lock the cooperating elements within the oil well casing, and when removed from the J-slots, release the cooperating elements from the oil well casing. As can be appreciated, this requires simultaneous functioning of the packer and bridge plug, which does not afford the independent setting and movement of the packer and bridge plug above and below the selectively isolated zone to be tested.